Neutrophil extracellular traps license macrophage production of chemokines to facilitate CD8+ T cell infiltration in obstruction-induced renal fibrosis

Renal fibrosis is a common mechanism leading to kidney failure in chronic kidney diseases (CKDs), including obstructive nephropathy (ON). Dysregulated inflammation is central to the development of renal fibrosis, but how local immune cells within the tissue microenvironment integrate and coordinate to drive this condition remains largely unknown. Herein, we documented that neutrophils were abundantly recruited and expelled neutrophil extracellular traps (NETs) in human and mouse fibrotic kidneys. Importantly, circulating levels of NET components displayed a significant correlation with worsened kidney function in ON patients. In the unilateral ureteral obstruction (UUO) mouse model, blocking NETs by protein-arginine deiminase type 4 (PAD4) deletion or DNase treatment significantly impaired NET formation and inhibited renal fibrosis and inflammation, whereas NET adoptive transfer exacerbated the fibrotic process. Moreover, NET-mediated renal fibrosis was associated with enhanced infiltration of cytotoxic CD8+ T cells, which produced granzyme B (GZMB) to drive tubular cell epithelial-mesenchymal transition (EMT) and fibroblast activation. Accordingly, pharmacological inhibition of GZMB resulted in blunted kidney inflammation and fibrosis. Furthermore, NETs profoundly potentiated the production of T-cell chemokines CXCL9/10/11 in macrophages, but not in tubular cells or fibroblasts, thus driving T-cell infiltration and fueling inflammatory cascades in the kidneys. Mechanistically, the NET-macrophage interaction was partially mediated by the TLR2/4 signaling. Thus, our work reveals a previously unexplored role of the collaboration between NETs and macrophages in supporting CD8+ T cell infiltration, which orchestrates kidney inflammation and fibrosis.